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Compression no longer working for some jobs

Created: 04 Nov 2013 | 3 comments

We have a number of jobs that run over the week. For some reason about a month ago our "Full" backup jobs began using much less compression. It went from a ratio of 1.5:1 to 1:1 or maybe 1.1:1. Our "Incremental" jobs are still compressing at 1.4:1. Does anyone have any idea why this is happening?

Things of note:
1. The tape drive is an HP StorageWorks 1/8 G2 Autoloader
2. All tapes are new HP LTO-5 Ultrium (C7975A)
3. All jobs (Full & Incremental) are set to compression type of "Hardware [if available, otherwise none]"
4. The "Enable Compression" check box on the drive config. is checked.

Thank you in advance for any help you can provide.


Operating Systems:

Comments 3 CommentsJump to latest comment

lmosla's picture

Are you using Symantec drivers for the tape drive?

and are all the updates installed from running Live Update?

pkh's picture

The most common reason for getting poor compression ratio is that you are compressing files which are already compressed, like zipped and move files, sound clips and pictures.  See my article below for an explanation.

1.4 - 1.5 are good compression ratios for a typical data mix.  What could have happenned in you case is that someone store some compressed files, like zipped files or pictures.  These get backed up with your full backup and cause a drop in compression ratio.  These are not changed and hence not backed up with your incremental backup and the compresssion ratio stays high.

Vishal Shinde's picture

Hello Jason,

Typically there are two types of compression used with Backup Exec, Hardware and Software Compression.

Hardware compression is done inside the tape drive by a chip that is designed to do data compression. All of the compression labor is done by that Drive.

Hence Backup Exec is NOT responsible for the compression; it merely switches ON the compression.

Compression is a solely controlled by the hardware.

Having said that, following factors contributes to the compression issues:

1. Bad tapes.

2. Type of data being backed up.

3. Tape header not cleaned for a long time.

Try using a new tape, rather a reused one and check the compression ration.

Kind Regards,


Vishal Shinde

Sr.Learning Consultant

Symantec Education Services